text:
Why did flight NH175 divert back to Los Angeles?
In the news recently is All Nippon Airways flight NH175, which returned to LAX after four hours towards NRT when it was discovered that a passenger aboard did not have the correct ticket, although his ticket was nevertheless to Tokyo. Two points immediately come to mind:

If a security issue was suspected, why did they not immediately begin diverting to the closest available airport that could accommodate a 777?
If there was no security issue, why did they not simply continue to Tokyo?

Perhaps another way to state the overall question is to ask why ANA protocol necessitates a return to the originating airport in this case.

That's actually very kind because if I boarded the wrong flight, I'd like to be let off where I boarded, rather than somewhere unfamiliar. This is especially important for a international flight since the passenger very likely does not have the traveling documents for the destination (Tokyo), so Tokyo is not a realistic option, unless the passenger OKs that.

@user3528438: Looks like the extra pax did in fact have a ticket to Tokyo. I've updated the question.

@jjack: From the flight track, it looks like anything on the West Coast from San Jose north would have been closer. Maybe even Anchorage.

If an airline knowingly carries someone into or out of a country who is not on their manifest they can be hit with serious fines.

Probably the crew wasn’t aware of the fact, that the passenger had a genuine ticket to Tokyo anyway. The saw probably just something like boarding pass and a person in front not on the passenger list. Maybe waiting some minutes would have been been enough for the ground personnel to figure out all the details. But nowadays - in the end - somebody will blame the pilot for being recklessly because of „terror“. Noteworthy, on some airports nobody cares about your passport, ticket nor boarding pass, they check you for weapons, bombs and drugs. But you can slip in every (low cost) plane.

@user3528438 - it may be kind to the passenger that made the mistake, it punishes the other  300 passengers on the plane that didn't make a mistake and they were forced to fly 8 hours to nowhere, then had to make arrangements for missed connections, hotel stays, etc. I don't know what the fine in Japan is for an undocumented traveler, but I think it's under $5000 in the USA, or around $15 per passenger, and I bet it cost the airline much more than that to accommodate everyone.

@Ben: That's a good point, but still why go all the way back to LA rather than divert to a closer US destination?

News reports are stating definitively that there was a security consideration. As for diverting to the nearest airport, it's not impossible that LA was extremely close to being the nearest airport.

@PeterSchilling I don't know, but I do know that I would sue the pants off them if they left my borderline-Alzheimers 85 year old grandmother alone in Anchorage because THEIR processes didn't work properly.

I doubt this question can be answered, as it’s a matter of company policy/decision making. I’m sure there was some communication back and forth between the pilots and the company after the mistake had been discovered. There’s no way of telling who made the call to turn back and why.

@TomMcW you may be right. Or perhaps surprisingly there will be someone one day who can answer, if the question is still open.

@Koyovis I have a suspicion that it was done intentionally. You can't tell me those two brothers didn't know what they were doing. They couldn't get two seats on the same flight, but who wants to be separated? I think it's a case of, "let's just see if they'll let me on with my Delta boarding pass. What's the worst that can happen? Hey, it worked!"


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Validity of Volga-Dnepr An-124 Grounding in US
Around June 10th, a Ukranian court issued an order grounding 5 of Volga-Dnepr's An-124 cargo planes, citing maintenance checks conducted without OEM (i.e., Antonov) authorization. According to FlightAware, one of those planes (tail no. RA-82078) has been sitting on the ramp at Huntsville International since June 26th, after landing in the U.S. for the first time since the court issued the grounding order. Has the FAA grounded that plane in response to the Ukranian court order, or are Volga-Dnepr leaving it there for other reasons? It's definitely not a grounding of all An-124s, since Antonov Airlines continues to operate An-124s in the U.S.

as you say, the grounding only involves 5 aircraft of one specific operator, so of course other operators aren't involved. As to why that one's sitting there, you'd have to ask the operator, or file a FOIA request with the FAA.

Regardless of what the FAA does, Volga-Dnepr would be in breach of the court order if it flew the plane anywhere in the world, and therefore subject to legal sanctions.

@David Richerby, Volga-Depnr's public position is (or at least was a few weeks ago) that the order has no validity outside the Ukraine and intend to continue operations regardless.

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What is the purpose of this interesting pattern of class E airspace in northwest Alaska?
Perusing SkyVector today I noticed this airspace pattern:

It can be viewed in more detail here.
What immediately jumped out at me is that

there are no charted airports in any of this airspace;
the RNAV routes crossing through this area are also class E, so in reality the airspace is not actually divided, but the VOR airway crossing in the northwest of the area gets different treatment; and
there is little discernible pattern to the airspace based on terrain, landmarks, or politics (e.g., it is more extensive to the north than to the south of the intersection, there is a very small extra bit in the southeast corner).

My best guess is that this airspace exists to facilitate IFR/VFR separation where three RNAV routes intersect, but that doesn't necessarily explain all the points above. I'm hoping that someone familiar with the area and/or better at searching FAA publications can lend some insight.

Inside the 8 charcteristic shapes, the Class G goes to 14,500' MSL, right?

This is easier to explain in reverse: rather than why there is so much class G airspace there, why is there so much class E airspace  everywhere else?
Remember, all airspace is class G unless it has been designated something higher. Wind your clock back to the early days of aviation, and the entire country was class G!
However, that isn't very safe, particularly in bad weather. Pilots were getting lost and running into each other.
So we got navaids and radios, and narrow strips of airspace along between navaids became controlled airways, i.e. class E. If you scroll over to Canada in SkyVector, you can see what this probably looked like.
Fast forward several decades, and there are now so many airways criss-crossing the US that they've merged into one big class E blanket, so it's easy to forget how we got here.
But there are still a few areas where the airway density never quite reached full saturation, mostly in mountainous terrain (of which Alaska has a lot), and those pockets still remain class G--and reveal the past.
As to why the V airway in your example has a different floor than the T airways, I'd assume that comes down to the minimum VOR reception altitude due to the terrain. Other than the floor, though, it's the same.

I have a follow-up question: why not make class E start everywhere at 1,200 AGL, abolish the blue vignette, get rid of high-altitude class G and simplify charts and rules? What would be lost? Do people really need to fly VFR in low visibility at high altitude in Alaska?

@scarpaz That explanation won’t fit in a comment, but feel free to ask a new question.

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How does the particular piece of flap behind an engine on a B777 work?
On several B77 photos, I notice that flaps just behind the engines are not always coordinated with the others flaps. On this photo flaps are extended but not behind the engine whereas on this photo all flaps are extended. Given the position of this particular flap, I suppose there is something to do with the interaction between flaps and engine. Given the difference between the two photos, it may also have something to do with spoiler extension.
EDIT: OK the two photos are not the same plane, but I find a video where it is obvious this piece of flap is not always coordinated with the rest of the flaps. When looking at the video I first thought it was a flaperon, but after the flaps are extended, it deflects upward several times without making the plane banking.

they are different models of planes, in the table below the first is a B777-333/ER while the second is a B777-222/ER,

It is called "inboard aileron" or "high-speed aileron" and is actually a flaperon. It will deflect with the flaps but not extend backwards. At high speed, the outboard ailerons are locked and all roll control is achieved by deflecting the inboard ailerons (and spoilers, if needed). This helps to reduce wing torsion and twist.
Background: Since the trailing edge's sweep angle has a break at the wing station of the engine, and since in Boeing aircraft the flaps extend perpendicularly to the hinge line, there must be a gap between inboard and outboard flaps, otherwise they would collide during extension. This gap is best placed in the station of the engine blast, and is filled with a simple hinged flap. Note that Airbus aircraft have rear-sliding flaps, which stay at a constant span location and can be adjacent to each other even at the wing station of the sweep change.

Boeing 767 from below. Picture by Adrian Pingstone (source)
The picture is of a Boeing 767, but shows the flap arrangement nicely. Note the offset of the forward and rear part of the Küchemann bodies which house the flap tracks.

I found other videos where we can see both this flaperon and the outboard ailerons. Indeed it is coordinated with other roll control surface (aileron and spoilers)

I disagree with that statement. The 737 has flaps that extend to be completely flush with each other, despite the fact they have non co-linear hinge lines. Why not use the same design for the flaps as a 737 and place the flaperon more outboard to achieve better roll control?

https://aviation.stackexchange.com/questions/66523/why-are-the-flaperons-on-the-787-located-so-far-in-board

You might find some answers on that here: https://aviation.stackexchange.com/questions/43093/how-do-the-uninterrupted-and-interrupted-flaps-compare .

What actually flaperon is used for? Some says that it is used for low speed (rather than high speed). Or, is it possible used for both?

@AirCraftLover: At high speed, the outboard ailerons are locked and all roll control is achieved by deflecting the inboard ailerons. This helps to reduce wing torsion and twist. At low speed it mostly serves as a flap.

@PeterKämpf thank you for your explanation.

To expand slightly on ratchet freak's comment, they're different models of plane, with different engines.  The first photo is a 777-300ER with General Electric engines (the only kind fitted on -300ERs); the second is a 777-200ER with Pratt and Whitney engines (one of three engine options). Looking at other photos, it appears that the flaps directly behind the engines of -300ERs don't extend nearly as far as those on the rest of the wing.
And note that there are significant differences between the -200ER and -300ER. For example,

the fuselage of the -300ER is 10m longer and the wingspan is 4m longer;
the -300ER seats 70+ more people;
the maximum take-off weight of the -300ER is about 40 tonnes higher.

That small part on the 777 is called a flaperon because it behaves like an aileron and a flap. It is particularly active during the landing phase where it is controlled by a function called "LAM", Landing Attitude Modifier. During other phases of flights, it stabilizes the plane in the roll axis, this method is more efficient because it creates less drag, making the plane more fuel-efficient. When the flaperon are not sufficient to maintain roll spoiler panels are then commanded by the flight computer (PFC).
That feature is a patent https://patents.google.com/patent/EP0809165A1
It is inactive during take-off below a certain speed (that I will not disclose as proprietary information).

You can tell us the speed, we won't tell anyone.

What's his behaviour when inactive? All the way down due to its weight? Free-floating int the airstream?

When inactive on the ground it just hangs down due to weight, the connected hydraulic actuator does not receive any pressure at all.

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Is the A380 ailerons' kinematic modified in alternate law?
I was looking at a video of a A380 display that led me to the "valse des ailerons". This strange ailerons behaviour is available in normal law, but what happen when some fly-by-wire features are not available (alternate law and direct law)? Is this kinematic still available or do all the aileron move together acting as if there was only one aileron per wing?
EDIT: As I received no responses but multiple good comments, I add some clarifications:
The "Valse des ailerons"' purpose and operating is documented in many places (see comments) but all those documentations assume the fly-by-wire system (sensors, actuators, computers,...) is healthy enough to stay in normal law. My question is: what happen when in alternate or direct law? Is there multiple cases, some in which the valse des ailerons is still available and some in which it is not?

Good video of this here, and a thread with discussion here.

Some additional explanation about wing load on the 747-8: http://youtu.be/c26y2-j5KrY?t=19m48s

The valse des ailerons is for gust alleviation. The local aileron deflection compensates gust loading on the wing, so it gets less dynamic loading. This increases structural life. I would not expect that this gust alleviation works also in direct mode (would be contradictory). Alternate law should also use gust alleviation, so the valse des ailerons would be displayed in alternate law as well. But I am guessing here, because I have no direct knowledge. That's why I post this as a comment and not as an answer.

@PeterKämpf My understanding is that you switch from normal to alternate/direct law when there are some problems. The Valse des ailerons require 3 fully functional ailerons per wing. There are cases where some ailerons or spoilers are not available. In those cases, the aircraft should switch to alternate/direct law. But there are cases where the ariplane switch to alternate law with all ailerons available (e.g. when freezing a Pitot tube or when loosing an angle of attack sensor). I agree in those cases, it may be relevant to keep the Valse des ailerons while being in alternate law.

Valse Des Ailerons (Waltz of Ailerons) or VDA is a nickname for the Load Alleviation Function (LAF) which is part of the flight control system. LAF uses all ailerons and spoiler 6 to 8 to alleviate the fatigue and static loads on the wings by reducing the wing bending moment.
It consist of various sub functions dealing with passive load alleviation (based on commanded load factor from normal law) and active load control based on measured accelerations in pylons under the wing.
From this it already follows that passive load alleviation requires normal law for load factor inputs.
There is a document circulating on the internet which seems to be an official Airbus Pilot Briefing for A380 pilots called "Flight Deck and Systems Briefing for pilots, issue 2". In the section about the Flight Control Systems under auxiliary system the following is said about the LAF:

Load Alleviation Function (LAF) The objective of the LAF is to reduce structure fatigue and static loads on the wing during maneuvers
  and turbulence. Spoilers 6 to 8 and all the ailerons are involved
  in the LAF.
The LAF is available in normal law only.

(Emphasis added by me)
So your feeling that Valse des Ailerons is only active in Normal Law is correct.

Update: Based on the A380 flight crew manual, it depends—

Nice document. Thanks for the extract that allow me to find it. I'm glad to see the bounty works well.

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What is happening with this aborted flight?
I live near Southend airport in the UK (SEN, EGMC) and noticed a strange behaviour of a cargo jet that does daily trips to Spain.  It started out on runway 05, took a normal departure until it turned around 5 minutes later.  Then it started circling the airport at 4,000' three times, before descending to 2000', switching direction and finally landing on runway 05.
The flight was obviously diverted back to Southend (it did leave an hour later) but given time was 0030-0100 local time, and it was quite noisy, can anyone think of a reason why it would repeatedly circle round a built up area so many times?
https://www.flightradar24.com/data/aircraft/g-powp#24941d80

edit:
There was a report on a local facebook group that it had lost communication, but its squawk didn't change to 7600

See if you can find the ATC recording, that's the only way to know.

@GdD It's illegal to record ATC in the UK, unfortunately, due to horribly outdated wiretapping laws that are still enforced by OFCOM.

Is it? I didn't know that @reirab, good to know.

@GdD Yep, it's bizarre, but it's true. It's why LiveATC doesn't have UK feeds.

Were they loud?  Probably a standard noise abatement flight.  They fly the airplanes around with the noisemakers set on "Max" every once in awhile, so the public will think all the other planes are quiet.

Lost comms doesn't necessarily mean squawking 7600, especially for an IFR flight.

Looking at the flight path the airplane departed consistent with a flight direct to Spain, then returned and was put into the holding pattern (I've flown that hold enough, it's where I do my recurrent instrument checkrides). The airplane then departed the hold and did the standard ILS approach for runway 05 before landing. The hold is in that location at least in part to keep airplanes clear of the most built-up parts of the area, and clear of the danger areas to the east.
My interpretation is that the pilots had a technical issue which meant they couldn't complete the flight, so they returned to the airport. They were put into the hold for one of 2 reasons:

To lose altitude. If a flight is too high a hold gives it time to descend while staying close to the airport
To allow another airplane to land ahead of them. Easyjet, Flybe and Air France fly out of Southend as well as cargo and charter operations, scheduled arrivals would get priority from Air Traffic Control. Scheduled commercial arrivals that is, they wouldn't put a 737 in a hold for me in a PA-28

A dire emergency would most likely have seen the airplane land without a hold, so it was most likely a non-emergency technical problem of some kind. The only way to know more would be to listen to the ATC recordings if there are any, although you could just try to call southend tower and ask, they are reasonably friendly.

My personal interpretation is that they were looking for backup ground signals.  There was no descent for 2 circuits, and no other traffic in the vicinity

During situations that require diverting back to the departure airport immediately after departure, it's also not uncommon for aircraft to request a hold for a while to run checklists and such before attempting the landing. Dumping fuel is another reason that might be done, though that seems unlikely here, as it normally wouldn't be needed on a flight from the UK to Spain and it wouldn't be done at low altitude over a populated area except in a pretty significant emergency where the aircraft didn't have time to hold during dumping.

@reirab instead of burning fuel, the holding can also be used to burn fuel (e.g. if the pilot want to stay close to the airport)

Unfortunately it is illegal to listen to ATC conversations in the UK.

It wasn't "circling around a built up area" - it was placed into a holding pattern.
At this point we can only speculate, but holding patterns are exactly as the name implies - aeroplanes obviously can't pull over and stop like a car can, so a holding pattern is a known position where they can just fly around without causing problems for other air traffic.
It could have been to sort something out on the ground, it could have been to give the pilots time to diagnose or work on the issue, it could have been giving time for the airport to handle the unexpected arrival.
It's next to impossible to guess - the only one I'd rule out is burning fuel as they look to have only done three patterns which is nowhere near enough to burn useful quantities of fuel.


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What exactly do winglets do?
I know that the winglets on planes like the Boeing B737 and Embraer E-190 reduce fuel consumption, but do they do more than that, or are they just for the stated purpose?

We expect you to do some basic research before asking here. Did you, for example, look at Wikipedia's article? If you did, and you didn't understand it, could you be a bit more specific about what you didn't understand? Then people will have something to work with.

They serve as a focus for modern cults.

The short answer is they exploit the flow circulating around the tip by generating lift that is oriented toward the fuselage, with a slight forward component because the local flow is slightly inboard as it curls around the tip, and lift is 90 degress to the flow.  They are basically sails, and were originally called "tip sails".  The result is a small thrust component, the same thrust component that propels a close hauled sailboat forward, and there is a downwash from the vertical wing that, being vertical, is actually an "outwash".  This outwash effectively turns some of the circulation field back in the other direction to a certain degree, weakening it.
They take the energy in the circulation and do useful work with it, in other words.


text:
What is the typical fuel consumption of a 737 in MPG?
What is the typical fuel consumption of a Boeing 737 in MPG?

Are you interested in MPG, or actually interested in things like emissions/mile or cost of fuel?  Emissions between a gallon of gasoline and gallon of jet fuel are close but not equal, and the cost is very different.

Which size of 'Gallon' are you interested in - there are at least two common definitions in use

The following table shows the long range cruise control data for a Boeing 737-800 (source: FCOMv1 Performance Inflight - All Engine PI.31.2):

Let us consider a typical cruise at FL370 with a weight of $ 65 \, \mathrm{t} $. The table tells us that the fuel flow per engine would be:
$$ \mathrm{FF} = 1231 \, \mathrm{kg}/\mathrm{h} $$
We are interested in the fuel consumption per distance, not per time. The table tells us that we would fly at Mach $ 0.793 $. At an altitude of $ 37 \, 000 \, \mathrm{ft} $ the speed of sound would be $ 295 \, \mathrm{m}/\mathrm{s} \approx 574 \, \mathrm{kt} $ assuming ISA (International Standard Atmosphere) conditions. This gives us the cruise TAS (true airspeed):
$$ \mathrm{KTAS} = 455 $$
The resulting fuel economy is then:
$$ \frac{2 \times \mathrm{FF}}{\mathrm{KTAS}} = 5.41 \, \mathrm{kg}/\mathrm{NM} $$
You asked for MPG (miles per gallon), so we need to convert that mass of fuel into a volume. The density of jet fuel depends on temperature. Assuming you refer to the volume on the ground, let us assume $ \rho = 0.820 \, \mathrm{kg}/\mathrm{l} $ for Jet-A. This gives:
$$ 1.51 \, \mathrm{gal}/\mathrm{mi} \; \Rightarrow \; 0.66 \, \mathrm{MPG} $$
All of this assumes no wind. If there is a $ 50 \, \mathrm{kt} $ headwind for example, the ground speed (GS) would reduce accordingly ($ \mathrm{GS} = \mathrm{TAS} - \mathrm{Headwind} $). Using this instead of KTAS in the equations above gives:
$$ 50 \, \mathrm{kt} \; \mathrm{Headwind}: \; 0.59 \, \mathrm{MPG} \; ; \; \; 50 \, \mathrm{kt} \; \mathrm{Tailwind}: \; 0.73 \, \mathrm{MPG} $$
Note: This is for the entire aircraft. If you are interested in fuel economy per seat, multiply the MPG with the number of seats (189 is the exit limit for a 737-800).


text:
Has automatic all-seat reclining been tested?
Seat reclining in modern economy-class seats is a problem when person in front of you reclines, but you are still in vertical position.
Has there been a consideration of simultaneous reclining of all the seats at the same time right after take-off?

I sure hope not. That would be awful. Can you imagine trying to read, or use a laptop?

I thought they were going out of their way to create a miserable experience.  The only way to make this worse would be to randomly move the seatbacks up at random intervals and speeds.

The only way? The low-cost airlines seem to be very creative in making a bad experience worse!

I can't imagine a manufacturer trying that for medical liability reasons; someone's back might be screwed up.

Your proposal would add several tons of weight to the aircraft by motorizing all the seats.

@Hobbes nah, just a latch that's released using a spring loaded mechanism. Seat drops back instantly, problem solved. Of course to put them up again someone'd have to go and recock the mechanism in each seat by hand :)

I'd much rather they remove the option to recline the seats at all. Problem solved, no more people slamming their seat back into your knees or chin. And all it'd take is a few spot welds :)

Some mobility impaired people may be very uncomfortable in the reclined position.


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Georgian Airways Flight Delay - Did LGW refuse flight and why?
Hi Our flight was delayed for 8 hours due to bad weather at Gatwick but there was no bad weather. I believe the airline was rejected by Gatwick due to a chance for holding if a storm came in. Is there a way to find out what ATC said to the airline???

ATC communication in the UK is not public: Is it illegal for Joe Public to listen to ATC in the UK?

Also, could you add which flight this was (flight number, day)?

As @Bianfable says, you should provide more informations about your scheduled flight so that we can make our own research about this flight.

You may edit either the question or its title to be coherent (one is asking about listening ATC  communication and the other is about decision made by company or crew)

Georgian Airways flight A9751 (Tbilisi to Gatwick) on the 19th of August indeed departed 7:30 hours late and arrived 7 hours late, according to FlightRadar24 records.
The exact cause of the delay is not public information. However, your theory that "ATC rejected the flight" seems highly improbable, since ATC can't actually do that. What could happen, is that flow control could impose ground delays to your flight to avoid airborne holdings later on if the capacity exceeds the demand. That could be the capacity at your destination, or at any of the countries your flight passes through on its way. So if, say, there were major thunder storms over Central Europe, a flight from Georgia to London might get caught up in that. However, 7:30 hour flow delays are almost unheard of, so that is probably not the (only) reason. My best bet would be technical or rostering issues, but that is only an educated guess.
If you really want to know the reason for delay, you should try contacting the airline


text:
If we add a video recorder in the cockpit to complete FDR/CVR, will we add a blackbox?
The introduction of a video recorder in addition to the current audio and flights parameters recorders used for crash investigation (CVR and FDR) is suggested by this article (published in the New York Times in 2004) citing officials of the National Transportation Safety Board, and called image recorder in a most wanted list (published in 2012) of the FAA.
Those two references shows the introduction of a video recorder is taken seriously. I don't want to debate whether this is usefull neither what should be recorded (wide angle of the whole cockpit, close view of switches and screens, black & white or color, ...).
Given the answers of this questions, the video track record's requirements should be very close to the one of the CVR, thus adding this track to the CVR seems reasonable.
If we add this video track to all tracks recorded by blackboxes, will this records to an existing blackbox (either the FDR or the CVR) or will we create a dedicated blackbox (resulting in three blackboxes)?

related questions :

Why could increases in cockpit voice and image recording potentially raise privacy concerns?
Why doesn't the black box also record video?

I don't think it's possible to answer this question clearly because in the end it's a matter of technical opinion and design. The 'best' answer might even be different for different aircraft models.

while your attempts to salvage this question are laudable, so far it has remained, in all its declinations, opinion-based: you are asking for an opinion about what might be done if and when a video track will be needed. Since no documentation is available, everything that can be produced as an answer is speculation and thus not a good fit for this site.

@Federico OK, I didn't understand. Given the only answer, I thought the opinion issue was on the necessity of adding the video track.

Before answering, let's look at these terms:
FDR - Flight Data Recorder
FDRs record all flight data, every button pressed, every control input etc. They record throughout the duration of the flight.
CVR - Cockpit Voice Recorder
CVRs record all voice communications through the radios and the chat pilots have between themselves. They record only the last 30-120 minutes.
So what benefit will adding a camera bring?
After an accident (God forbid) the investigators are not interested to see what was the color of pilot's shirt or was he picking his nose before he pressed a button. In addition, you would need several cameras to record every single action of the pilots, and even then it would be hard to figure out as some buttons are placed very close to each other.
FDRs solve this problem as any input from the pilots are recorded. CVRs capture all communications so the motive or reason behind any input from pilots are be found out.

I suggest you to read some NSTB investigation reports (here or here) to get a detailed idea how in-depth knowledge the investigators can get by these two instruments.

FDR's don't record all flight data, only a limited set and at a limited rate. IIRC, currently 88 parameters need to be recorded in new build planes.

Your answer focuses on whether or not it's useful and practical to have cameras in the cockpit, but that's not actually the question that the OP asked.

I do not agree. It could be very informative to see that a pilot was distracted by something, or was looking at his charts when something happened. Even if a pilot was in the seat at some point in time (or is there a sensor in the chair?)

The NTSB disagrees with you, at least insofar that, for the past couple decades, one of their recommendations has consistently been for the FAA to require image recorders in aircraft cockpits.

@Sean 1) Please provide a reference about NTSB recommending FAA. 2) I did not say that cameras are not needed. I stated that there won't be much value in capturing data elements which FDR and CVR are already capturing. 3) Yes, there will be value in adding cameras, but there several cameras will be needed to capture all motions in a cockpit.

@Farhan: Here you go - Safety Recommendations A-15-007 (superseding A-00-030) and A-15-008 (superseding A-00-031).


text:
Is it possible to have V1 greater then Vr?
According to wikipedia, decision speed ($V_1$) is computed taking into account the runway length (and other parameters). If an aircraft uses a long runway (one listed here), there may be enough runway available to stop an aircraft rejecting takeoff at high speed. Thus $V_1$ can be higher than usual, perhaps greater than $V_r$ or $V_2$. Is the situation where $V_1$ is greater than $V_r$ possible?

See: http://aviation.stackexchange.com/a/3567/258 If Vr is ever less than V1 then Vr will be increased to equal V1.

I think the answer is no.
If you think about V1 as primarily based on runway length, it is certainly possible for an aircraft to easily reach Vr long before reaching the "point of no return" as far as stopping distance is concerned.
However, you must also consider the meaning of Vr. This is when the aircraft is going to rotate. After rotation and leaving the ground, the distance required to still stop on that same runway increases significantly.  For this reason, maximum V1 is generally considered to be Vr (see this discussion).
In large aircraft, rejecting a takeoff after leaving the ground is generally discouraged, unless the pilot feels that the plane could be uncontrollable. It's much safer to continue the takeoff and fly for a normal approach. However, it can happen.
In smaller aircraft, it's more reasonable for the aircraft to take off and then land safely (I'm thinking a C172 on one of the low density altitude runways you linked to).

For smaller aircrafts operating on way oversized strips it is different. Still, mine is a "niptcking"reasoning.

The "this discussion" link goes to the airliners.net forum homepage.

@Sean thanks for the correction and heads up on the link. FYI, I'm fixing them by searching the link on the wayback machine, then googling some of the text to find the new location.

Simply no
Rotation comes always after decision :)


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Is it possible to selectively deactivate alarms?
My question is restricted to Airbus an Boeing's best sellers, namely the A320 and the B737. If relevant, answer can be extended to other types.
In those aircraft, there are multiple possible alarms (GPWS, stall warning, unwanted altitude excursion,...). Some alarms may be triggered by faulty sensors and deactivated. As an example, I can cite the "Too low! Gear!" of the TK1951 due to faulty radio altimeter. When identifying an alarm is a false alarm, it should be nice to deactivate this alarm and only this alarm. My understanding is that you can mute an alarm when triggered but nothing prevent this alarm to be triggered again later in the flight, but I don't know if my understanding is right.
Is it possible (technically) to deactivate a specific alarm (let's say "Too low! gear!") for the rest of the flight after identifying this is a false alarm? In other word, is it possible to prevent a specific alarm from being triggered without impacting the other alarms?
EDIT: the main difference with the question Can pilots turn off warning alarms? Re: Aeroperu Flight 603 is that I want to know if an alarm can be turned off for the remaining of the flight, not only "whilst the condition exists.".

This isn't a duplicate, can someone reopen?


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Why is 51,000 ft a common service ceiling for business jets?
According to this article on aerospace-technology.com, many of the larger business jets seem to have a service ceiling of 51,000 feet. Other sources verify this trend.
What is the reason for this, if anything specific can be named? Some possibilities that I came up with are:

engineering considerations (limitations of materials, pressurization, systems capabilities etc.)
safety, i.e. time of usefull consciousness getting too short higher up (being less than 10 s @ 50,000ft)
too little to be gained going higher (no congestion anymore at that alt anyway)
an industry agreement (based on any of previous and/or other factors), in the same manner as european automakers' pact to limit the max speed of cars to 250km/h (excluding some model)
regulatory factors

Other common "steps" appear to be 45,000 ft and 41,000, with smaller models. Nice round numbers all, but surely there has to be some reason for the magical 51,000 ft figure. Interestingly, the Learjet 85 was designed to have a service ceiling of "only" 49,000 ft, and the program got cancelled at least partially due to poor sales. It seems it was simply lacking the last 2000 ft...

Examples of business jets with 51000ft service ceiling:
Cessna Citation X
Falcon 7X, 8X
Global  5000, 6000 and 7500
Gulfstream G550, G600, G650 ER
Learjet 40, 45, 60, 70/75
etc...

„european automakers' pact to limit the max speed of cars to 250km/h“. The rumor says it is some sort of gentleman’s agreement, Porsche is not following it. In europe Vmax is Vmax not Vtemporary. Sustaining higher speed becomes technical challenging. You need spoilers and/or ESP (remember Audi TT). Tires with speed index V are affordable, higher speed indices like ZR or Y are expensive. I like my german Autobahns with Richtgeschwindigkeit as they are - they are not speedways! Aside physics, personal exhaustion is quickly reached, traffic (jams) and environmental conditions limit it.

TT was kind of a special case, a beautiful and futuristic car, but the form of the back was such that it created lift at high speeds. Good for planes, bad for cars... I've driven cars with absolutely no problem reaching or maintaining the 250km/h limit. Many carmakers would be able to surpass that speed with relative ease, but it was easier, safer and more profitable just to make an agreement to keep thingd to a certain limit. The 51,000 feet ceiling could be a similar case.

@Peter: I'm having trouble seeing how even a high-speed car would require the use of extrasensory perception in order to drive; did you mean ESC (electronic stability control)?

@Sean many car makers actually use abbreviation ESP for car stability control: https://en.m.wikipedia.org/wiki/Electronic_stability_control#Product_names And it always makes me smile.

ESP, ESC, DSC or vehicle dynamics controls. ESP is the trademark of Bosch. To be honest, I didn’t knew that their so many terms for this ;)

I've had by far the most fun in cars with the aforementioned turned off...

If for no other reason, its likely because there is a practical maximum descent speed for a given airframe and aircraft must be able to descend from their maximum cruising altitude to 10,000 ft. in 10 minutes or less. Although under part 135 (how many of these planes are likely flown) the regulations have a few variations you can have less oxygen on board if you can descend in 4 minutes.
At 51,000 ft. you would need to lose 41,000 ft in 10 minutes or even 4 minutes. That is a descent rate of either 4100 ft/min or a blistering 10,250 ft/min which likely yields a speed at or near Vne for most of these airframes.
This Gulfstream pilot discusses a bit of it from a practical standpoint here.

The Gulfstream pilot -link is excellent!! It shows (among other things) through several examples how complex this issue is from regulatory point of view.

Plus the thing that did not come to my mind (the graph + table earlier in the article), above ~45000 feet TUC stays pretty much the same: all the oxygen you have is in your blood, you can't breath in any extra from atmospheric conditions, but TUC does not diminish that fast either.

You could also point out that at 63000 feet blood boils at normal body temperature, which means if you go above the low 50s without a pressure suit you are getting dangerously close to instant death if you get a decompression.

So Concorde could do it because it could descend at high speed. Makes sense. I wonder if Concorde ever had such an event.

@John K So Concorde was really pushing it at FL600?

@TomMcW yes, sort of. For example  one of the reasons concorde had such small windows was that if one of them broke, the pressure loss would be slower.

@JohnK if you are referring to the Armstrong limit, no, blood would not boil because of blood pressure, not even close. Saliva, sweat and moisture in the lungs would. Fun fact: If you were flying at or above the Armstrong limit without pressurisation, and (as your last deed) decided to take a leak, you would piss steam.

@Jpe61 yes thanks for the correction.  It might be better to say you'd get the bends right away.   The bends could be a problem for some unpressurized aircrew in WW2 at 25000ft.


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Is wingtip design mature?
There are many wingtip design, all made to reduce vortex related drag, and neither boeing nor airbus seems to prefer one over another. They move from one design to another at each new aircraft, always claiming the new choice is more efficient than the previous one. In detailed, all generation mixed, it looks like (non exhaustive list):
winglet: B737NG, A330, B747-400, A320NEO, A350
wingtip fence: A320, A380, B737MAX
raked wingtip: B787
EDIT: The other elements of aircraft design are almost the same for all new aircraft (low wing, engines under the wing, classical landing gear, APU in the tail, ...), so I assume it has reached a great level of maturity, nothing has to be improved and introduced on a new aircraft generation. This is obviously not the case for wingtip.

Different designs function in different manners, although they tackle one issue, which is how to deal with wingtip vortices.

"almost all the same"? They're no more the same than the wing tip design is the same.

An EXCELLENT question. I think the fierce debate that it generated stands testimony to the excellence of this question.

The wingtips are a unique part of the aircraft in that they really have one job; minimize drag. Their design is easy to see, and they are a fairly recent addition to transport aircraft. Developments continue to be made in the study of aerodynamics, with modern computing power and methods allowing much better modeling of flow patterns to evaluate designs, and improvements in materials allowing more complex designs to be built.
The key is that the winglet must be properly designed. As wing designs change, the flow over the wings changes, and new winglet designs are invented.
Since it is heavily dependent on the specific application, it's more relevant to look at the evolution of the designs on different aircraft. The design chosen is dependent on the technology available at the time, both for evaluating the design and building it, the design of the wing, intended use of the aircraft, and the previous experience of the manufacturer.
The 737 is an old design that has evolved over time: Original/Classic: none, NG: winglet, P-8: raked tip, MAX: split scimitar
The A330 is a fairly new design: Current: small winglet, neo: winglet
The 747 has also evolved over time, and the latest version shares technology with the 787: Original: none, -400: small winglet, -8: raked tip
The A320 has also evolved over time: Original: none, Current: tip fence, neo: winglet
The A380 is a new design: tip fence
The A350 is a new design: winglet
The 787 is a new design: raked tip
The 777 is a fairly new design: Basic: none, -200LR and -300ER: raked tips
You will notice a trend from smaller designs to larger ones. On larger aircraft though, the weight of a large winglet and the loads it produces can get too large. New designs like the 777, A380, 787, and 747-8 all use either raked tips or small winglets.
As for other parts of aircraft, engines are changing more than you think. The jet engines on the early jet transports look very different from modern high-bypass turbofans. The GEnx engines on the 787 and 747-8 have chevrons at the back to reduce noise. All you see on the outside is the nacelle that minimizes drag; most of the changes go on inside. Also, if you look closely at the front, fan blades on newer engines have curves in them instead of having straight edges.
Most other parts of the aircraft have more complex jobs, not primarily external. A fuselage should be efficient at carrying things inside but also keep drag low. If you look closely you will notice that new planes like the 787 and A350 have a lot in common with previous fuselages, but they are shaped differently as well. It's harder to see the other drastic changes like the use of composites in place of traditional aluminum, electric systems instead of hydraulic or bleed air, fly by wire, etc.
Control surfaces must provide sufficient control while minimizing drag. The size and shape has also changed over time, though the general design has remained.

I accessed the paper and cannot find the exact quote, but I feel that the final remark is even more relevant: It is clear that the benefits are far reaching. If properly designed, such that the profile drag penalty is of no consequence over the range of speeds at which the sailplane operates, there are no reasons to not take advantage of the benefits that winglets offer in both performance and handling qualities

Or even this, from the previous section: In designing winglets for a variety of sailplanes, as well as for a number of nonsailplanes, it appears that all wings can be improved with winglets.

... but not in performance, only in handling. The benefits are in roll rate (true) and spin resistance (depends), and carry a big "if": Profile drag must be low. That is not easy. Remember: Winglets cause drag, but no direct lift. How should that improve performance? In airplanes which fly mostly straight and as fast as possible?

It is interesting to see how well that "winglet snake oil" works, without a shred of evidence. People defend it even with made-up quotes, or by taking quotes out of context. This looks to me like a religious war.

@PeterKämpf not in performance, only in handling that's your claim, the referenced paper clearly shows an improvement of L/D ratio and cross-coutry speed. So far you have not reported any source demonstrating the contrary, by what is written here, you are selling the "snake oil".

@Federico: Open your eyes: This is true only with span restriction in competition classes. Man, I am getting tired fighting your ignorance. Go and preach your misunderstood nonsense, but I will no longer respond.

@PeterKämpf if you want to fight ignorance, use data, not presumed authority. Yes, I see the limitations of that paper, but they in no way support your claims.

The original 737s came from the factory sans winglets, but the 737-200 now has an aftermarket "mini" winglet.  The split-scimitar design is for the NGs, not the MAXs; the MAXs use a different style of double winglet, known as the Advanced Technology (AT) winglet.  Most of the NGs still have the simple blended winglets, though (which can also be fitted to the Classic 737s).  See here.

I'm not an aeronautical engineer, so this answer may contain errors.
The design of an aircraft pretty much is the design of a wing. The fact that wingtip designs change is only due to the fact that wing design changes with every aircraft type as well.
Fuselage design is mature in the sense that circular is better than square. Engine design is mature in the sense that engines are interchangeable; as long as you've got the correct hardpoints on the wing for fuel, bleed air, and so on, it doesn't matter whether you choose to install the Wilbur 400 turbofan or the Orville 602N turbofan.
But the wing is integral to the aircraft. For each airliner you design, you design a wing to go with it. Center of gravity, center of pressure, critical mach, all of these things and lots more are taken into account and each are different for each aircraft, so they have to be addressed differently. The fact that wingtips differ from model to model only means that wings differ from model to model.

It really doesn't matter that much.
Look at birds: They use two different wingtip designs. I guess we will both agree that those designs are mature after millions of years of evolution. And still there are two distinct wing tip shapes: One is the "fingered" wingtip with large, spread-out feathers, and one is the pointed tip you find from seagulls to albatrosses, and also in swallows. Why is there not one, mature design?
This has to do with the environment they are used in. Seabirds and swallows fly in an unobstructed environment with steady winds and need to stay aloft for longer duration. All other birds, also lake-dwellers like Pelicans, have to cope with trees obstructing a straight flight path and gusts from hills, or those trees. They need to maneuver quickly and cope with gusty winds. This is helped by a reduced span and the possibility to fold the outer wing in or fan it out in an instance. Hence the fingered wingtip.
For most aircraft, the seabird solution should work best. But sometimes the environment adds new demands, like span restrictions in the competition classes of gliders. Then it makes sense to add a winglet.
Another "restriction" is the high cost of developing a new wing, not to speak of the tooling and certification effort. Then it helps to add a winglet so the outer wing can contribute more lift if the aircraft mass is increased by stretching beyond the capabilities of the original wing. But this will drive up wing bending moments disproportionally, so the overall benefit is small. It will always be better for performance to design a new wing with a straight wingtip.
If you see all kinds of fancy winglets on modern airliners, this has to do more with marketing than with aerodynamics. After all, no bird has winglets. Not a single one.
But now picture the Airbus board (full of bean counters and lawyers, and void of aerodynamicists) after Boeing has hyped up their new wingleted wing: The immediate reaction is: We need this wonder device, too! But it must look different! Sadly, this has led to the quasi-religious following of the winglet cult, where winglets are made to be the cure-all of aerodynamic problems.
Now one can argue that nature never came around to try the winglet modification. Not in more than 100 million years, not in one of several independent developments of wings (pterodactyls, insects, birds and bats. You can even add fish to that list, their flippers have a similar function). This could be, but now the question comes down to Occam's Razor: Which is more likely?

Nature never developed winglets, despite their advantages? And please don't call the elastic deformation of tip feathers winglets. This is plain silly.
Or Nasa and Boeing marketing have hyped up a device which does improve aerodynamics in some conditions, but is not as good as a straight wing extension if the conditions allow for that extension?

Judge for yourself.

The no bird has winglets (implying that are useless and thus airplanes should follow suit) is a logical fallacy of humongous proportions.

@Federico: Why? Just because you claim it is? Or is there any substance to this claim?

@PeterKämpf because is a huge misinterpretation and misrepresentation of how evolution works. ask a biologist, I cannot summarize the principles of evolution in a comment section on aviation.SE. Also, by that same logic no bird has jet engines.

@Federico: Don't confuse the inability of life to evolve rotational mechanics with optimum shaping of wings. Bending wingtips upwards is well within the possibilities of avian evolution, but never brought a selective advantage. Not in pterodactyls, nor in insects, bats or birds. Or fish fins, for that matter.

the fact that no random mutation has produced a winglet* in birds is in no way a demonstration that airplanes do not benefit from them, there is no logical relationship. [*even though the "fanned" design you refer, such as the eagle's, can be considered a form of optimum winglet]

@Federico: So you consider evolved wings as not mature. The winglet modification is just waiting to happen? Nature never tried it, in >100 million years of biological flight? Could be, yes. But is extremely unlikely. That settles it for me, I will no longer reply to your baiting.

So you consider evolved wings as not mature implying that somehow is. That's what I referred to when I said that you misinterpret and misrepresent the evolutionary process. I reiterate my invitation to speak with a biologist. (or to support your answer's claims with sources)

I normally look forward to your answers, Peter. I believe I have learned more in this SE from your answers than just about anyone else. I find it very difficult to believe that either of the major manufacturers would have spent manhours and money testing and designing, and installing, wingtip modifications unless there is a benefit other than 'marketing.' Seems to me that if wingtip mods were 21st Century snake oil, that one or both of (Airbus and Boeing) would have left them off their designs.

Dudes, dudes ... point 1 ... many birds have winglets ..!!! Point 2, (in agreement with Federico) there are many many features of wings, that have, utterly no counterpart in the evolved wing world.  Point 3, some parts of this are like "The spandrels of San Marco" (ie, equally confused, in similar ways ;-) )  * ducks *

Regarding "21st century snake oil". I feel you are completely wrong, CG. (You're not cynical enough for this world :) ) It's totally commonplace that billion-dollar seemingly engineering-driven entities, utilise "pure, ridiculous, snake-oil."

@JoeBlow: I can only support your view. Boeing engineers spent several months on optimizing the fuselage-stabilizer intersection of the 767, only to have one manager impose a different geometry "because the optimized one looks like McDonnell-Douglas". Stuff like this is commonplace. Unfortunately. And if it looks to you that birds have winglets: The feathers bend upwards like any flexible wing does. This still does not make them into winglets.

interesting anecdote!  I'm afraid I feel it's true for better or worse -- well in my opinion.  In the 90s I worked briefly in the software dept. of a jet engine research outfit near Berlin. The whole effort was gimmick driven :)  I worked in advertising for some years, and it's common for eg pharma companies to spend literally billions on something as thin as "well this name! sounds like blah so we can make a lot of money if we spin out some sort for product around that!"  Regarding automobiles it's not even worth mentioning examples :-)

@JoeBlow but in this case the numbers do not support the "snake oil" story, see the paper cited in the other answer.

@Federico: Look at my comment regarding the paper. The quoted sentence is nowhere to be found in it.

I know, I read the paper and quoted other sentences from it, see my comments.

@JoeBlow: Thanks for mentioning the "Spandrels of St. Marco", I learned something new! But unfortunately, this paper is provocative, but mostly wrong, see Robert Mark and many others.

hi @PeterKämpf!  I think you may have misunderstood me: the "Spandrels of St. Marco" is indeed famous as one of the WORST and most-WRONG papers in science, by a famous guy!!  So, please read again, I said "this discussion is like spandrels of st marco - very confused!"  :-)  for the definitive discussion on "spandrels of st marco" - surely Richard Dawkins.  {Regarding that paper, in a word, I think the funniest thing is THAT, IN FACT, there ARE obviously and everywhere "in-between" spandrels! Heh! For the rest see Dawkins.}

BTW this site rocks, you guys are all amazing. So much info on this site!

@PeterKämpf, "Looks like McDonnell-Douglas" could very well mean "McDonnell-Douglas has a patent on this intersection design, and will sue us if we use it".  Quotes taken out of context can be highly misleading.

@Mark: I talked to the engineers involved, and that was NOT what they said. The manager was simply determined to have a different look so that Boeing does not corroborate the work of their (then) competitor.

There, I asked for you.

your "evolutionary" arguments are still wrong, as reported in the linked biology.SE question. "nature" has no way of trying the winglets, either all intermediate steps are better than the current version, or the local minima is retained, even if the global minima is somewhere else.

@Federico: I know, any of my arguments will be wrong if they do not support the superiority of winglets. I have got your point and take the liberty to disagree. With facts. But those do not count in religious disputes. That's why I now really stop responding.

@PeterKämpf could you please realize that I do not care about winglets and that I care about: 1- wrong biology statements 2- wrong logic. You can demonstrate that winglets are the root of all evil in the world for what I care, but not using wrong evolutionary comparisons in a manner devoid of any logic.

It is wrong to suggest that the winglets on the Airbus A380 are a fashion accessory. Its is such a big plane that conventional wings would have been too wide for many airports. Winglets improve the efficiency of the wing tip, allowing a shorter span for the same overall performance. Airbus found that the length of winglet was very similar to the reduction in span, so in effect they just turned the tips upwards without loss of performance. It was purely a practical engineering decision.

@GuyInchbald but then nature has no artificial span restrictions. You are right, winglets help when span is limited, see this answer for example. In the absence of arbitrary regulations winglets make no sense.

@PeterKampf - the first part of which is precisely why your comparison with nature is meaningless, but that is a criticism already made. Note that it was not regulations but ground infrastructure which dictated the Airbus decision. There are other reasons to use winglets and related tip devices, but one counter-example to your misplaced suggestion is enough.

@PeterKampf Well, if you like pedantry then ICAO classes are descriptive not regulatory. Moreover, as you acknowledge they apply to the ground infrastructure not to the plane.


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What are the pro/cons of polyhedral cranked wings?
Dihedral wings seems to be very common (almost if not all low-wing airliners, many modern gliders,...). Polyhedral seems to be less common and mainly found in relatively old aircraft (F4 Phatom, F4U Corsair, DR400,...). By polyhedral, I mean at least 2 dihedral angle with a sharp discontinuity between both. I don't include wings whose diheadral angle varies smoothly along the wingspan (such as this B787).
But I was surprised to discover that this design (polyhedral with sharp angle between the distinct diheadral sections of the wing) was elected in at least 2 project whose first flight was in the last 10 years (namely the solar impulse and the qinetiq zephyr). I do realize that both examples I gave have similar missions (stay airborne as long as possible, and thus fly slowly; gather as many sun-energy as possible, and thus fly as horizontally as possible) and may thus have similar design.
Given recently-designed aircraft with polyhedral wing exist, what are the pro/cons of such design over well spread dihedral wings and over the smoothly varying dihedral angle?
EDIT: note that the polyhedral does not necesseraly increase the dihedral angle as we go away from the wing root (Be 12, Habicht,...)

While dihedral wings offer increased stability in the roll axis, they also decrease the lift that the wings provide. A polyhedral wing provides a compromise: a steep dihedral at the tip of the wing in order to maximize stability, and a shallower dihedral angle closer to the root in order to maximize lift.

Therefore, a polyhedral wing allows the best of both worlds for a wing design. Other applications of a polyhedral wing are utilitarian; the gull wing on the Vaught F4U Corsair is designed so that the landing gear is positioned close to the ground while maintaining roll stability and aerodynamics.

Sorry, I can't help it.  I can't look at the wing on a Corsair without feeling, all, funny, ooo err, it's happening again, nurse, nurse!  The  cannot hold it is too late.  The light is blinding, my ears hurt, oh man, there it goes again,,,,for pitys.......sake.......help.......me.......

Oh man, @Simon has lost it! Darn, he wrote really good answers!

@Timpanus I'm quite confused. Your answer says dihedral increase roll stability. But this website, this answer, this one and this one say that it provides slip-roll coupling (and not roll stability).

@ManuH: It's both, depending. The increase in roll stability is primarily due to the CG being effectively lowered due to a dihedral effectively raising the wing by raising the wingtips (some may explain roll stability to be due to one wing being straighter in a bank but that explanation is false). On a low wing aircraft (like WW2 fighters) dihedral may not increase roll stability but only neutralise it (from negative roll stability due to low wing). Actually.. now that I've written it, I guess increasing roll stability from negative to zero is technically increasing it. So, yeah.

I always thought that the Corsair's distinctive wings were a way to keep the enormous prop away from the ground while using relatively short landing gear.  But I don't recall an authoritative source for that.  It's just one of those things I always heard.

Another advantage for the Corsair's gull wing is pilot visibility.

Polyhedral wings are used in aircraft for various reasons, mainly to improve roll stability without significant change in the overall wing design.

The original design of the F-4 Phantom (which started as a 'super F3' had a constant swept wing with anhedral.

By U.S. Navy - U.S. Navy National Museum of Naval Aviation photo No. 1996.253.7320.028, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24564607
However, wind tunnel tests indicated stability problems, which were were overcome with giving the outer wings a 12$^\circ$ dihedral, corresponding to a 3$^\circ$ overall (with changes in wing sweep too). This saved a major redesign of the wing, while also allowing the spar to pass below the fuselage.

Another example of this is the Antonov An-12 'Cub'. The early prototypes had a straight high wing. However, test flights showed the aircraft having poor lateral and longitudinal stability, which was remedied by increasing anhedral on the outer wing panels.

By Sefjo - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=29397593

The F-4U Corsair had polyhedral wings as the the designers had to keep the landing gear short enough, while at the same time have enough ground clearance for the huge propeller used.

Re "The original design of the F-4 Phantom (which started as a 'super F3' had a constant swept wing with anhedral."-can you give a source for the idea that original design wing had anhedral? I have never heard that before.  (Have heard that the dihedral angle of the tips was a later addition to fix stability issues.) I hope that you are not basing that "anhedral" idea solely on the included photo, as it is very difficult to assess the 3-d geometry of a wing from a single view at that sort of angle. In my opinion the geometry of the wing in that photo might be completely flat (no dihed or anh.)

Lets consider the dihedral angle from three points of view:

Stability, the more conventional one, it mainly influences spiral stability, which is the tendency of the aircraft to enter into a spiral due to a perturbation (i.e.: gust): The aircraft should not enter this spiral, it is allowed to enter in a spiral only when the motion  is slow enough for the pilot to safely recover.
Reduction of induced drag, a more "unconventional" aspect to analyse the dihedral angle, requires higher dihedral angles.
Integration, keeping  clearance between the ground and the wing tip and/or engines/propellers. This is specially important for the ground phases.

From the stability point of view the dihedral main effect is on the $C_{l_{\beta}}$ (and $C_{l_{r}}$) derivative. This derivative plays a major role (along with other such as ($C_{n_{r}}$ $C_{l_{p}}$, $C_{n_{p}}$, $C_{n_{r}}$) in defining the spiral and dutch-roll modes.
These other derivatives usually depends heavily on the design of the vertical stabilizer design (except $C_{l_{p}}$, which is mainly influenced by aspect ratio). Since the vertical stabiliser design is more complex than trading the dihedral angle (whose main influence is on $C_{l_{\beta}}$) , the latter can be used to "adjust" the desired spiral and dutch-roll modes, to desired values.
The dihedral angle, when exaggerated, has a secondary effect on induced drag as well. This can be seen from the configuration on the bottom right in the figure below. Here it can be noted how a  (very) high dihedral angle has a positive effect on the aerodyanmic efficiency factor $\epsilon$. Generalizing, the higher the displacement of the wing (the dihedral angle) the better it is for induced drag (think about the new B787 or A350 designs). Since induced drag is the main component of drag in low speed, and since the aircraft you mentioned (solar impulse, kinetiq zephir), are solar powered and flying slowly I can imagine that they have a stronger use case to minimize drag.
Finally the dihedral angle can be used to mitigate "integration" problems. The other example you mentioned I think fall in this category. On the Beriev Be 12,the propellers would be too close to the water, expecially when the aircraft is floating (see here). And similar the Habicht wihtout the gull wing would have a wing tip too close to the ground.

Your third bullet point ends rather abru

Also, second to last paragraph: "The secon aspect is to consider the dihedral angle". Should that be "The second aspect..."?  There are enough terms I'm not 100% sure on that I'm not comfortable just making the edit myself.  /proofreader

Polyhedrals are good for enhancing spiral stability, but also used for faster response pitch stability.  Since polyhedral effect on spiral stability is simple to understand, I'll describe the polyhedral's effect on pitch stability with respect to speed.  This produces speed stability through pitch as follows:
In order to minimize the induced drag a typical downward lifting tailplane produces, designers may employ lifting tailplanes on models like the familiar Guillow's "Arrow," or the contest models like "Witch Doctor" or "Ramrod."  In these models the plans specify the CG to be placed near the main wing training edge, far from the center of main wing lift.
The tail is lifting in these models, so the lift between the main wing and tailplane must provide the same pitching moments for zero pitch rate in stable flight.
But this means that there is no typical speed on pitch stability due to the difference in incidence (decalage angle) between tailplane and wing.  The wing to tail decalage is significant on these models, but cannot aid pitch stabile because both wing and tail lift vectors are oriented in the same direction.  Instead, like a conventional design with a forward CG, the total increase in lift causes upward translation with no initial pitch rotation.
When this happens, the AOA on all main wing panels and tail plane is reduced since the airplane has an upward velocity component in the slipstream, resulting from this upward translation (without rotation in pitch).  The result is that the entire wingspan and all the wing panels of the polyhedral have less difference between them in AOA.  Contrast this with slow flight, where the outer panels can have 0º AOA while the inner panels have high AOA. That variation of AOA in the various polyhedral wing sections as a function of Wing centerline AOA is the operating principle used.
This means, depending upon how the aircraft is trimmed for speed, the disparity in how much of the main wing is producing lift changes significantly from low to high speed flight.  This provides faster response pitch on speed stability than would be achieved with normal pitch on speed stability derived from a typical forward CG.
If the outer panels go to 0º AOA near high centerline AOA (slow flight) main wing lift decreases enough to quickly bring the nose down.
This means that the model will have innate spiral stability as well as a very precise pitch on speed stability that can be adjusted to ensure the aircraft seeks its most efficient speed far more quickly than other non polyhedral designs.
So the result is much more precise pitch positive dynamic stability (shorter phugoid wavelength) than a non polyhedral which has to wait for a second order response in pitch stability due to the mechanism of classic pitch stability for conventional forward CG configurations.


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Do wing warmers exist?
In moto racing, they use tire warmer to keep tires hot when the tire is not running.
In particular weather conditions (e.g. heavy snow), aircraft require de-icing operation after staying parked for few tenth of minutes.
Do any device to protect the wings and other parts of the aircraft requiring to be free from ice before take off from icing and possibly keeping those parts above icing temperature exist? It could save some deicing time (and de-icing fluid) by reducing the amount of ice accumulated while the aircraft is on the ground.
EDIT: When asking the question, I was thinking of airliners between two legs in winter in Canada (with jetbridge connected, only few tenth of minutes before next scheduled leg, international airport ground support available,... and snow and icing conditions). I don't think the question should be restricited to this case, but it should take it into account.

There is something called a hangar that does just that.

In certain conditions, if a plane has sat long enough, it will be de-iced more than once as needed.

I would imagine that most answers will be something along the lines of "if integrated heaters were installed, the energy consumption and weight of such devices would cost more in fuel to transport them for every flight than they would save in time not being deiced". There's also the "the time and money spent by the airport/airlines to purchase, store, inspect, install and remove external covers (for every potential aircraft) is greater than the time and money spent to run through the deicing shower (that fits all aircraft) prior to take off".

@SMSvonderTann Airliners are rarely put into hangar between two legs as they are grounded for only few tenth of minutes.

@ManuH Well, that comment was put before you edited your question to say that.

@SMS Commercial aircraft are rarely hangared ever.  Hangar space is at a premium at all major commercial airports and is mainly used for maintenance.  It would also be prohibitively expensive (in terms of time and therefore lost utilisation plus ground handling fees plus hangarage fees) to put them to bed and wake them up every time they needed to go flying.  The airport would also need many more tugs and the taxiways would be jammed.  It's just not practical to hangar a commercial jet.

Wow, I've hear of tight turn around times, but thenth of a minute? We're talking 6 seconds here! :) I realize English isn't your first language and I say that jokingly. I think you mean tens of minutes - more than 10, but (usually) less than an hour. Intended to be helpful, not insulting. English is hard, even for native speakers - I cringe when I hear many Americans speak.

The standard solution for keeping aircraft parts "above icing temperature" when on the ground is, as was pointed out in the comments, a nice heated hangar.
This has the secondary benefit of keeping all the other components at a warmer temperature where they're more amenable to operating (gyros spin up better, wheel bearings rotate more easily, etc.)
Once outside of a hangar deicing fluid is used, and provides "anti-icing" protection for a specific period (the fluid's "holdover time") - we discussed that in more detail on this question.
Obviously once the aircraft has been exposed to icing conditions or snowfall for a period exceeding that holdover time it must be de-iced again as there is a chance for ice to begin accumulating.
There is also the potential to use the aircraft's ice protection systems (in particular electro-thermal systems such as used in the Boeing 787 which heat the wing in the manner you allude to in your question), though I'm not aware if any systems are currently approved to be used in this way.
One of the key challenges there would be verifying that the wing surface is indeed free of ice, snow, and frost - that's easy to do from the deicing truck (particularly since deicing fluid is tinted so you can see where it has been applied), but on a typical passenger jet the pilots can't see the wing from the cockpit, and poor visibility from blowing snow, fog, etc. may make the visual determination difficult from the cabin as well.


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What is the THS deflection speed?
Let's restrict this question to best sellers airliners (A320 and B737). On  this aircrafts, the THS is used for pitch trim. The speed requirements may not be has intense as for elevator as it control a longer term action. I excpect the elevator to act quickly (I imagine less than half a second from full up to full down, several degrees per seconds) but what about the THS? Does this speed change depending on the flight phase? (I see no reason, but I may be mistaken)
This question is restricted to autotrim function (otherwise, I think the speed of pilots hands may be the limiting factor)

The speed varies depending on which system is operating the trim, e.g. the mach trim might be slower than what the autopilot can trim or the speed trim system that counteres the pitch moments of the flaps but the fastest rate would be manual electric trim. I'd estimate the trim speed to be less than one degree per second because of the way it is actuated, via jack-screw.

@Jan clarified.

For the A320:

Conf 0/1 the rate is 0.3°/s
Conf 1+F/2/3/Full the rate is 0.7°/s

I haven't found any difference for A/P vs Manual flight.
In A319, THS freezes in the following situations:

The pilot enters a manual trim order.
The radio altitude is below 50 ft (100 ft with autopilot engaged).
The load factor goes below 0.5 g.
The aircraft is under high-speed or high-Mach protection.

In A320, THS freezes in the following situations:

The pilot enters a manual trim order.
The radio altitude is below 50 ft (100 ft with autopilot engaged).
The load factor goes below 0.5 g.

There are further conditions under which THS range is limited, let me know if you would like me to expand.
Source: A320 FCOM DSC-27-20

Using the Boeing 737NG as an example:
When the flaps are up,  the pilots' electric trim switches operate at 0.2 units per second (low-speed trim).  Otherwise, they operate at 0.4 units per second (high-speed trim.)
With the autopilot engaged, the low & high speeds change to 0.09 & 0.27 units per second, respectively, depending on the flaps setting.
Note: the THS angles are reflected in "Aircraft Nose Up" (ANU) units, which in Boeing's convention, 1 unit ANU = 1 degree deflection.  While THS angles can be negative, ANU units are always positive.  On the NG, the full range of the THS is 17.1 degrees (from -4.2° nose down to 12.9° nose up), which is mapped to 0 - 17.10 ANU units.
Source: 737NG AMM, HORIZONTAL STABILIZER TRIM CONTROL SYSTEM - ELECTRIC TRIM - FUNCTIONAL DESCRIPTION.